1. Field of the Invention
The present invention relates to the preparation of diorganopolysiloxanes having alkoxy end groups, referred to hereinafter as PF (polymers containing functional groups), and their particular use as one of the essential constituents of single-component organopolysiloxane elastomeric compositions which are stable in storage in the absence of moisture, but which crosslink on exposure to atmospheric moisture at ambient temperature, hereinafter designated cold vulcanizable elastomeric (CVE) compositions.
2. Description of the Prior Art
A variety of processes are known to this art for the preparation of diorganopolysiloxanes having alkoxy end groups. Compare, for example, the processes described in U.S. Pat. Nos. 3,122,522, 3,161,614 and Re. 29,760. The processes described in these patents are not employed industrially at the present time, because they are either too costly or provide PFs of poor quality for their essential use as a base polymer for CVE compositions.
A major advance in the art is described in U.S. Pat. No. 3,542,901, namely, a process for the preparation of PF by reacting an alpha,omega-dihydroxydiorganopolysiloxane polymer, in other words a diorganopolysiloxane having silanol end groups, with a polyalkoxysilane in the presence of a catalyst for functionalization with an amine group.
This process is undoubtedly efficient, but it is very difficult to effectively remove the amine, which may have a detrimental effect on the storage stability of the CVE composition in the presence of the condensation catalyst, which is a metal, typically tin compound.
Other catalysts may be used, such as, for example, an organic titanium derivative (U.S. Pat. No. 4,111,890), an alkoxyaluminum chelate (British Pat. No. 2,144,758) and a N,N-disubstituted hydroxylamine (French Pat. No. 2,508,467, U.S. Pat. No. 4,472,551). These catalysts may present the disadvantage of poor efficiency or of having a detrimental influence on the storage stability of the CVE compositions.
Another process for producing PFs uses mixed silanes which, in addition to the alkoxy groups, contain a hydrolyzable group, such as an amido, amino, carbamate or oxime group, or the like, optionally in the presence of a known functionalization catalyst and a polyalkoxysilane.
Processes of this type are described particularly in U.S. Pat. Nos. 3,697,568, 3,896,079 and EP-A No. 69,256.
These processes are efficient, but require the use of costly mixed silanes. Furthermore, the organic compounds provided by the hydrolyzable groups after the reaction can have a detrimental effect on the CVE composition (see, on this subject, pages 4 and 5 of French Pat. No. 2,543,562).